An apparatus according to the present invention can be used to supplement a conventional central heating boiler using a liquid circuit by recovering the heat from the off-gases and transferring their energy to the heating liquid which is normally water. This apparatus can either be incorporated detachably in the flue gas duct, or, if desired, it can also form an integral part of the boiler.
A similar device is described in NL-A-7612508, but in addition to the elements set forth above, that device also consists of a heating device for off gases that have already been cooled, while the fan has the added capability of adding fresh air. By condensing water from the flue gas that device achieves a substantial heat transfer from the flue gas to the returning heating water. However, the description of that device states that it is necessary to reheat the cooled flue gas and to supply fresh air to prevent condensation in the flue. This, of course, involves a loss of efficiency and requires additional fan capacity. Therefore, that design is less suited for the construction of a very compact but yet accessible unit which can be made relatively cheaply through mass production.
One object of the present invention is to provide an apparatus for recovering energy which overcomes the disadvantages of the device disclosed in NL-A-7612508. Thus, a suitable apparatus must have the following properties:
(1) a good heat transfer capacity,
(2) good condensation properties for the water of the flue gas,
(3) a slight resistance for the flue gas with little occasion for fouling, and
(4) simple initial installation procedure.
Additionally, the apparatus must also have the following design features:
(1) a simple design, aimed at mass production,
(2) a compact design, requiring a short overall length and little space, and
(3) a design permitting essential parts to be overhauled and cleaned in a simplified manner.